FIG. 1A illustrates an exemplary prior art probing system used to test dies (not shown) on a newly manufactured semiconductor wafer 112 or other electronic devices. The probing system of FIG. 1A includes a test head 104 and a prober 102 (which is shown with a cut-away 126 to provide a partial view of the inside of the prober 102). To test the dies (not shown) of the semiconductor wafer 112, the wafer 112 is placed on a moveable stage 106 as shown in FIG. 1A, and the stage 106 is moved such that terminals (not shown) on dies (not shown) of the wafer 112 are brought into contact with probes 124 of a probe card assembly 108. Temporary electrical connections are thus established between the probes 124 and dies (not shown) of the wafer 112 to be tested.
Typically, a cable 110 or other communication means connects a tester (not shown) with the test head 104. Electrical connectors 114 electrically connect the test head 104 with the probe card assembly 108. The probe card assembly 108 shown in FIG. 1A includes a wiring board 120, which can provide electrical connections from connectors 114 to the probe substrate 122, and the probe substrate can provide electrical connections to the probes 124.
The cable 110, test head 104, and electrical connectors 114 thus provide electrical paths between the tester (not shown) and the probe card assembly 108, and the probe card assembly 108 extends those electrical paths to the probes 124. Thus, while the probes 124 are in contact with the terminals (not shown) of the dies (not shown) on the wafer 112, cable 110, test head 104, electrical connectors 114, and probe card assembly 108 provide a plurality of electrical paths between the tester (not shown) and the dies (not shown). The tester (not shown) writes test data through these electrical paths to the dies (not shown), and response data generated by the dies (not shown) in response to the test data is returned to the tester (not shown) through these electrical paths.
It is often advantageous to test the dies (not shown) of the wafer 112 at specific temperatures or over a range of temperatures. To this end, heating elements or cooling elements (not shown) may be included in the stage 106 or at other locations in the prober 102 to heat or cool the wafer 112 during testing. Even if heating elements or cooling elements (not shown) are not used, operation of the dies (not shown) of the wafer 112 may generate heat. Such heating or cooling from either heating/cooling elements (not shown) or from operation of the dies (not shown) may cause the wafer 112 and the probe substrate 122 to expand or contract, changing the positions of the probes 124 and the terminals (not shown) on the wafer 112, which may cause misalignment between the probes 124 and terminals (not shown) in a plane that is generally horizontal in FIG. 1A. (This horizontal plane is in the directions labeled “x, y” in FIG. 1A and will hereinafter be referred to as “x, y” movement. In FIG. 1A, the direction labeled “x” is horizontal across the page, the direction labeled “y” is horizontal into and out of the page, and the direction labeled “z” is vertical. These directions are relative and for convenience and are not to be taken as limiting.) If such “x, y” misalignment becomes too great, the probes 124 will no longer be able to contact all of the terminals (not shown).
The use of heating elements or cooling elements (not shown) to heat or cool the wafer 112 during testing, and/or the generation of heat by the dies of the wafer 112 as they are tested, may also cause a thermal gradient between the side of the probe card assembly 108 that faces the wafer 112 (hereinafter a side of the probe card assembly that faces the wafer 112 will be referred to as the “front-side” or the “wafer-side”) and the opposite side of the probe card assembly (hereinafter the opposite side of the probe card assembly will be referred to as the “back-side” or the “tester side”). Such thermal gradients can cause the probe card assembly 108 to bow or warp. If such bowing is towards the wafer 112, the probe card assembly 108 may press against the wafer 112 with too much force and damage the wafer 112 or probe card assembly 108. If such bowing is away from the wafer 112, some or all of the probes 124 may move (in a generally vertical direction with respect to FIG. 1A) out of contact with the terminals (not shown) on the wafer 12. If the probes 124 do not contact the terminals (not shown), the dies (not shown) on the wafer 112 will falsely test as failed. (Movement to or away from the wafer 112 is labeled the “z” direction in FIG. 1A and will hereinafter be referred to as “z” movement.)
Often, immediately following installation of a probe card assembly 108 in a prober 102 with a heated (or cooled) stage 106, the probe card assembly 108 will undergo thermally induced movement. The movement stops and the position of the probe card assembly 108 stabilizes only after a sufficient temperature equilibrium is reached between the front-side and back-side of the probe card assembly 108. Of course, such an equilibrium need not be a perfect equilibrium in which the front-side temperature of the probe card assembly 108 exactly equals the back-side temperature; rather, the front-side temperature and the back-side temperature need only be sufficiently close that the structure of the probe card assembly 108 is able to resist thermal movement. The time required to reach such a temperature equilibrium or near equilibrium is often referred to as “thermal equilibrium time” or “thermal soak time.”
Typically, the probe substrate 122 is attached directly to the wiring board 120, which in turn is attached to a test head plate 121 on the prober 102. A shown in FIG. 1B, the test head plate 121 forms an opening 132 in the prober 102 into which the probe substrate 122 fits (as generally shown in FIG. 1A). The test head plate 121 may include holes 134 for bolts that secure the probe card assembly 108 to the test head plate 121. (Clamping or techniques other than bolting may be used to attached the probe card assembly 108 to the test head plate 121.) The wiring board 120 is typically made of a printed circuit board material, which is particularly susceptible to thermally induced “x, y” and “z” movements. Improved techniques for counteracting thermally induced movements (including “x, y” movement and “z” movement) of a probe card assembly and reducing thermal equilibrium time would be desirable.